Chapter 3 Problems

ECET 214Prof. Park

NJIT

Problem 1

Which of the following is not an advantage of a synchronous detection?

a. Low distortionb. Eliminate diagonal clippingc. Greater ability to follow fast-modulated signalsd. Ability to produce gain

Problem 2

The mixer is often referred to as:

a. RF amplifierb. oscillator generatorc. second detectord. first detector

Problem 3

Varactor diodes are used for tuning by:

a. capacitance adjustment through a reverse bias diode.b. capacitance adjustment through forward bias.c. temperature compensation of diodes.d. all of the above.

Problem 4

In a varactor diode, as voltage increases, capacitance:

a. increasesb. stays the samec. decreasesd. none of the above

Problem 5

The only roadblock to having complete receivers on a chip aside from station selection and volume controls is:

a. limiting factors of tuned circuits.b. local oscillator.c. mixer circuits.d. IF amplifier.

Problem 6

The radio receiver that simply consists of an RF amplifier, detector, and audio amplifier is known as:

a. a superheterodyne receiverb. a TRF receiverc. a selective receiverd. a sensitive receiver

Problem 7

A receiver’s sensitivity is:

a. the extent to which a receiver is capable of differentiating between the desired signal and other signals.

b. its ability to drive the output speaker to an acceptable level.

c. the ability of the receiver to demodulate a modulated signal.

d. the ability of a receiver to attenuate noise signals.

Problem 8

A receiver’s selectivity is:

a. the extent to which a receiver is capable of differentiating between the desired signal and other signals.

b. its ability to drive the output speaker to an acceptable level.

c. the ability of the receiver to demodulate a modulated signal.

d. the ability of a receiver to attenuate noise signals.

Problem 9

If a receiver is overly selective:

a. too much noise is picked up and amplified by the receiver.b. only part of the bandwidth of the AM signal is amplified,

causing some of the sideband information to be lost and distortion results.

c. the tank circuits within the tuned amplifiers have insufficient Q.

d. when the volume control is turned up to maximum, the desired station is very weak.

Problem 10

If a receiver is underselective:

a. only part of the bandwidth of the AM signal is amplified, causing some of the sideband information to be lost and distortion results.

b. the tank circuits within the tuned amplifiers have too high a Q.

c. when the volume control is turned up to maximum, the desired station is very weak.

d. more than one radio station on different frequencies may be picked up by the receiver at the same time.

Problem 11

A TRF receiver is to be designed with a single tuned circuit using an 8.2 uH inductor. If the frequency is to be tuned from 550 kHz to 1600 kHz, find the BW that results at 550 kHz if there is exactly 10 kHz BW at a frequency of 1050 kHz.

a. 105 kHzb. 15.24 kHzc. 5.24 kHzd. 10 kHz

Problem 12

The diode detector:

a. is one of the simplest and most effective AM detectors.

b. consists of a nonlinear diode and low-pass filter.

c. is sometimes referred to as an envelope detector.

d. all of the above.

Problem 13

Which is not an advantage of diode detectors?

a. Power absorbed from the tuned circuit by the diode detector reduces the Q of the tuned circuit.

b. They develop a readily usable dc voltage for automatic gain control circuits.

c. They are highly efficient.d. Distortion decreases as the amplitude of the AM

signal increases.

Problem 14

Diagonal clipping:

a. occurs if the time constant of the low-pass filter is too large compared to the period of the RF waveform.

b. is a type of distortion that occurs with diode detectors.

c. is characterized by having the capacitor voltage not follow the full changes of the envelope of the AM waveform.

d. all of the above.

Problem 15

Synchronous detectors:

a. are often called product detectors.b. offer low distortion compared to diode

detectors.c. have the ability to provide gain.d. all of the above.

Problem 16

The superheterodyne receiver design is superior to the TRF design:

a. since it allows for a constant selectivity over the entire tuning range of the receiver.

b. since it always uses synchronous detectors instead of diode detectors.

c. since it uses many RF amplifier stages before the RF signal is mixed with the local oscillator signal.

d. all of the above.

Problem 17

An AM signal having a carrier frequency of 560 kHz is to be mixed with a local oscillator signal at a frequency of 1035 kHz. What does the output of the IF amplifier consist of?

a. a 455 kHz carrierb. a 475 kHz sinewavec. a 475 kHz AM signald. the original intelligence signal

Problem 18

In Figure 3-1, the output signal of stage (e) is:

a. an AM signal with a carrier frequency of 490 kHz.

b. an AM signal with a carrier frequency of 1850 kHz.

c. a 490 kHz sinewave.d. an 1850 kHz sinewave.

Problem 19

In Figure 3-1, the output signal of stage (d) is:

a. an AM signal with a carrier frequency of 490 kHz.

b. an AM signal with a carrier frequency of 1360 kHz.

c. a 490 kHz sinewave.d. a 1 kHz sinewave.

Problem 20

In Figure 3-1, the output of stage (a) is:

a. an AM signal with a carrier frequency of 1360 kHz.

b. an AM signal with a carrier frequency of 1850 kHz.

c. a 490 kHz sinewave.d. an 1850 kHz sinewave.

Problem 21

In Figure 3-1, the output signal of stage (c) is:

a. an AM signal with a carrier signal of 490 kHz.

b. an AM signal with a carrier frequency of 1360 kHz.

c. a 490 kHz sinewave.d. a 1 kHz sinewave.

Problem 22

In Figure 3-1, the receiver design is known as:

a. regenerativeb. superheterodynec. TRFd. synchronous

Problem 23

In Figure 3-1, the stage sometimes referred to as the first detector is:

a. stage ab. stage bc. stage cd. stage d

Problem 24

In Figure 3-1, the stages that contain tuned circuits are:

a. stages a, b and d.b. stages a, b and c.c. stages a, d and e.d. stages a, c and d.

Problem 25

In Figure 3-1, the stages that must contain nonlinear devices are:

a. stages a, b and c.b. stages a and e.c. stages b and d.d. stages b and c.

Problem 26

In Figure 3-1, the imagefrequency would be:

a. 980 kHzb. 2340 kHzc. 1850 kHzd. 870 kHz

Problem 27

A padder capacitor:

a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.

b. is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band.

c. is placed in an RF amplifier to provide for proper neutralization.

d. is placed in a tank circuit to provide for electronic tuning.

Problem 28

A trimmer capacitor:

a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.

b. is placed in parallel with each section of the ganged capacitor of the tank to provide tracking at the high end of a large frequency band.

c. is placed in an RF amplifier to provide for proper neutralization.

d. is placed in a tank circuit to provide for electronic tuning.

Problem 29

A varicap:

a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.

b. is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band.

c. is placed in an RF amplifier to provide for proper neutralization.

d. is placed in a tank circuit to provide for electronic tuning.

Problem 31

Image frequency rejection on a standard AM broadcastband receiver is not a major problem since:

a. the image frequency is not close to the IF frequency.b. the image frequency is not close to the LO frequency.c. the image frequency is not produced by mixing action.d. the image frequency is so far away from the RF

amplifier stage’s tuned frequency.

Problem 32

Which of the following is not a major benefit ofusing RF amplifier stages in superheterodynereceiver design?

a. improved image frequency rejectionb. larger frequency tuning rangec. more gain resulting in improved sensitivityd. improved noise characteristics

Problem 33

Which of the following is not an advantage of FETsover BJTs in RF amplifier usage?

a. Their input impedance does not load down the Q of the circuit preceding the FET stage.

b. The availability of dual gate FETs provides an isolated injection point for the AGC.

c. Their input/output square-law relationship allows for lower distortion levels.

d. They have improved image frequency rejection.

Problem 34

An autodyne mixer is:

a. a stage that provides the mixing and generates the LO at the same time.

b. a mixer that uses a dual-gate FET.c. a mixer that automatically provides for AGC action.d. a stage that mixes the LO with the AM signal without

the use of a transistor.

Problem 35

In a superheterodyne receiver the bulk of thereceiver’s sensitivity and selectivity is due to the:

a. RF amplifier stages.b. converter stages.c. IF amplifier stages.d. local oscillator.

Problem 36

Double conversion is:

a. a receiver design that uses two superheterodyne receivers to receive a weak signal.

b. a technique used to reduce image frequency problems in a superheterodyne receiver.

c. a technique used to solve the TRF tuning problems.d. a method that ensures that a superheterodyne

receiver does not break into oscillations due to stray positive feedback.

Problem 37

The circuit of Figure 3-2 is anexample of:

a. an RF mixer, local oscillator, and IF filter

b. an autodyne mixerc. a receive converterd. all of the above

Problem 38

In Figure 3-2, the tank circuitmade up of L1 and C1 istuned at:

a. the IF frequency.b. the LO frequency.c. the RF carrier frequency.d. the image frequency.

Problem 39

In Figure 3-2, the tank circuitmade up of L4 and C4 istuned at:

a. the IF frequency.b. the LO frequency.c. the RF carrier frequency.d. the image frequency.

Problem 40

In Figure 3-2, the tank circuitmade up of L5 and C5 istuned at:

a. the IF frequency.b. the LO frequency.c. the RF carrier frequency.d. the image frequency.

Problem 41

In Figure 3-2, the purpose of C3 is:

a. to determine the frequency of oscillation of the LO.

b. to couple the local oscillator frequency from the tank circuit to be amplified by Q1.

c. to act as a bypass capacitor for R3.

d. to neutralize the RF amplifier stage.

Problem 42

The AGC control voltage:

a. is actually the dc voltage component produced by the mixing action in the AM demodulator stage.

b. varies as the signal strength of the received signal varies.

c. is a negative feedback voltage.d. is produced by an RC circuit having a much larger time

constant than that of the detector.e. all of the above.

Problem 43

In Figure 3-3, the tank circuit made up of L1, A, and B is tuned to:a. the LO frequency.b. the RF carrier frequency.c. the IF frequency.d. the image frequency.

Problem 44

In Figure 3-3, the tank circuit made up of L4, C, and D is tuned to: a. the LO frequency.b. the RF carrier frequency.c. the IF frequency.d. the image frequency.

Problem 45

In Figure 3-3, the tank circuit inside of T1 is tuned to:a. the LO frequency.b. the RF carrier frequency.c. the IF frequency.d. the image frequency.

Problem 46

In Figure 3-3, the transistor Q1 is used as:a. the nonlinear device in an RF mixer stage.b. the active part of an RF amplifier.c. the active part of an LO stage.d. all of the above.

Problem 47

In Figure 3-3, the transistor Q2 is used as:a. an RF mixer stage transistor.b. an IF amplifier stage transistor.c. a detector transistor.d. an audio amplifier stage transistor.

Problem 48

In Figure 3-3, the transistor Q3 is used as:a. an RF mixer stage transistor.b. an IF amplifier stage transistor.c. a detector transistor.d. an audio amplifier stage transistor.

Problem 49

In Figure 3-3, the transistor Q4 is used as:a. an RF mixer stage transistor.b. an IF amplifier stage transistor.c. a detector transistor.d. an audio amplifier stage transistor.

Problem 50

In Figure 3-3, the AM demodulation is accomplished by:a. transistor - Q3.b. diode - E1.c. diode - E2.d. transistor - Q4.

Problem 51

In Figure 3-3, the filter that produces the AGC voltage consists of:a. R11 and C11.b. R5 and C4.c. R11 and C12.d. R10 and C10.

Problem 52

In Figure 3-3, the inductors L1 and L2 function as:a. an IF transformer.b. a loopstick antenna.c. part of the local oscillator.d. a nonlinear mixer.

Problem 53

In Figure 3-3, the transformer, T3, is tuned to:a. the intelligence frequencies.b. the RF carrier frequency of the received station.c. the IF frequency.d. the local oscillator frequency.

Problem 54

In Figure 3-3, the selectivity is accomplished by:a. T1, T2, and T3.b. L1 and L2.c. L3 and L4.d. R11 and C11.

Problem 55

In Figure 3-3, E1 functions as:a. an auxillary AGC diode.b. a mixer diode.c. an AM detector diode.d. an IF amplifier diode.

Problem 56

In Figure 3-3, the volume is controlled by adjusting:a. T3b. R12c. capacitors B and Dd. R17

Problem 57

The reference level for the unit, dBm, is:

a. the milliwatt.b. the milliampere.c. the watt.d. the millivolt.

Problem 58

In Figure 3-4, the powerdriven into the audioamplifier stage is:

a. 2.51W.b. 2.51 mW.c. 0.398 mW.d. 398 mW.

Problem 59

The conversion gain ofthe mixer in Figure 3-4 is:

a. -81 dBb. 3 dBc. -3 dBd. -78 dB

Problem 60

The total gain of the entirereceiver in Figure 3-4 fromthe antenna input to theaudio amplifier output is:

a. 89 dB.b. 59 dB.c. 119 dB.d. 30 dBm.

Problem 61

The power gain of theaudio amplifier in Figure 3-4 expressed as a ratioquantity is approximately:

a. 1000.b. 2512.c. 34 dB.d. 30 dBm.

Problem 62

A receiver has a dynamic range of 65 dB. It has asensitivity of 0.88 nW. The maximum allowableinput signal is approximately:

a. 1.56 uW.b. 278 mW.c. 2.78 mW.d. 156 uW.

Problem 63

A receiver has a maximum input signal of 75mW before distortion occurs. Its sensitivity ismeasured to be 1.5 nW. Its dynamic range isapproximately:

a. 47 dB.b. 77 dB.c. 154 dB.d. 87 dB.

Problem 64

Good troubleshooting practice says:

a. perform a visual check and check the power supply voltages.

b. prepare a trouble reportc. log the serial and model numberd. check the power supply voltagese. none of the above

Problem 65

Electronics Workbench Multisim provides a featurethat allows for the addition of a component fault ina circuit. This is accomplished by:

a. replacing the part with an F-prefix partb. replacing the part with a non model partc. double-clicking on the component, select fault and

specify the type of failured. all of the abovee. none of the above